Fix AssertionError on incompatible scopes with impl typealias

This has been introduced in 9ecd04f628

compiler/frontend/src/org/jetbrains/kotlin/resolve/checkers/HeaderImplDeclarationChecker.kt

@@ -143,7 +143,9 @@ object HeaderImplDeclarationChecker : DeclarationChecker {
         // TODO: replace with 'singleOrNull' as soon as multi-module diagnostic tests are refactored
         val singleIncompatibility = compatibility.keys.firstOrNull()
         if (singleIncompatibility is Incompatible.ClassScopes) {
-            assert(descriptor is ClassDescriptor) { "Incompatible.ClassScopes is only possible for a class: $descriptor" }
+            assert(descriptor is ClassDescriptor || descriptor is TypeAliasDescriptor) {
+                "Incompatible.ClassScopes is only possible for a class or a typealias: $descriptor"
+            }
 
             // Do not report "header members are not implemented" for those header members, for which there's a clear
             // (albeit maybe incompatible) single implementation suspect, declared in the impl class.
@@ -162,8 +164,11 @@ object HeaderImplDeclarationChecker : DeclarationChecker {
             val nonTrivialUnimplemented = singleIncompatibility.unimplemented.filterNot(::hasSingleImplSuspect)
 
             if (nonTrivialUnimplemented.isNotEmpty()) {
+                val classDescriptor =
+                        (descriptor as? TypeAliasDescriptor)?.expandedType?.constructor?.declarationDescriptor as? ClassDescriptor
+                        ?: (descriptor as ClassDescriptor)
                 diagnosticHolder.report(Errors.HEADER_CLASS_MEMBERS_ARE_NOT_IMPLEMENTED.on(
-                        reportOn, descriptor as ClassDescriptor, nonTrivialUnimplemented
+                        reportOn, classDescriptor, nonTrivialUnimplemented
                 ))
             }
         }

compiler/testData/multiplatform/regressions/incompatibleClassScopesWithImplTypeAlias/common.kt

@@ -0,0 +1,3 @@
+package test
+
+header abstract class Writer protected constructor()

compiler/testData/multiplatform/regressions/incompatibleClassScopesWithImplTypeAlias/jvm.kt

@@ -0,0 +1,3 @@
+package test
+
+impl typealias Writer = java.io.Writer

compiler/testData/multiplatform/regressions/incompatibleClassScopesWithImplTypeAlias/output.txt

@@ -0,0 +1,18 @@
+-- Common --
+Exit code: OK
+Output:
+
+-- JVM --
+Exit code: COMPILATION_ERROR
+Output:
+compiler/testData/multiplatform/regressions/incompatibleClassScopesWithImplTypeAlias/jvm.kt:3:1: error: 'impl' class 'Writer' has no implementation of 'header' class members:
+
+    protected constructor Writer()
+
+    The following declaration is incompatible because visibility is different:
+        protected/*protected and package*/ constructor Writer()
+    The following declaration is incompatible because number of value parameters is different:
+        protected/*protected and package*/ constructor Writer(p0: Any!)
+
+impl typealias Writer = java.io.Writer
+^

compiler/tests/org/jetbrains/kotlin/multiplatform/MultiPlatformIntegrationTestGenerated.java

@@ -206,6 +206,12 @@ public class MultiPlatformIntegrationTestGenerated extends AbstractMultiPlatform
             KotlinTestUtils.assertAllTestsPresentByMetadata(this.getClass(), new File("compiler/testData/multiplatform/regressions"), Pattern.compile("^([^\\.]+)$"), TargetBackend.ANY, true);
         }
 
+        @TestMetadata("incompatibleClassScopesWithImplTypeAlias")
+        public void testIncompatibleClassScopesWithImplTypeAlias() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/multiplatform/regressions/incompatibleClassScopesWithImplTypeAlias/");
+            doTest(fileName);
+        }
+
         @TestMetadata("kt17001")
         public void testKt17001() throws Exception {
             String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/multiplatform/regressions/kt17001/");